1. Field of the Invention
This invention relates generally to neutron-capture, primarily in boron-10, therapy (hereinafter BNCT) treatment of cancerous tumors, and more particularly to apparatus and method for conducting such therapy.
It is desirable that BNCT be accomplished effectively at a low cost of generation of neutron beams with minimal side effects such as caused by gamma (.gamma.) rays or "thermal", "epithermal", and "fast" neutrons. Typical energy ranges of these three neutron groups are: thermal .ltoreq.1 eV, epithermal 1 eV to 50 keV, fast .gtoreq.50 keV.
In my view, this can be achieved by providing a low-power reactor, with patients placed close to the reactor to have adequate beam intensity, notwithstanding the low power. Neutron beam optimization over a short distance between the reactor core and the patient is then required. The neutrons emerging from the reactor/moderator assembly should already be what is needed for the BNCT.
2. Description of the Prior Art
Boron-neutron-capture therapy (BNCT) has been known as having potential for treatment of cancerous tumors for more than thirty years. In such therapy, there are two primary components, both of which need to be optimized during the development of the procedure.
The first is a chemical boron (B-10) compound which is preferentially deposited in tumors. The second is a beam of neutrons which preferentially reacts with B-10 in the tumor.
Capture of a neutron in B-10 splits the compound nucleus B-11 boron-11) into two nuclei, He-4 (helium-4) and Li-7 (lithium-7), with energies of 1.5 and 1.0 MeV, respectively. Both nuclei lose their energy over a short distance, largely within a single cell. The damage through ionization during the slowing down of these two nuclei destroys the tumor cell with a high probability. For the destroyed cell to be, again with a high probability, a cancer cell, requires the combined maximization of the preferential deposition of boron in tumors and the preferential exposure of the tumor to neutrons of the right energy.
Alternatives to boron capture are also being considered. One alternative is the fissioning of a U-235 (uranium-235) nucleus, resulting in two fission products which can also destroy the host cell.
Some background and recent thinking on the subject of BNCT are described in two articles which have recently appeared in the publication entitled Nuclear Science and Engineering. One of them (hereinafter referred to as "Ref. 1.") is by Otto K. Harling et al., Volume 110 (1992), pages 330-348. The other (hereinafter referred to as "Ref. 2.") is by Manfred Papaspyrou and Ludwig E. Feinendegen in Volume 110, pages 349-354. The Harling et al. article has a FIG. 1 illustration of the five megawatt Massachusetts Institute of Technology Reactor (MITR) arranged for medical therapy. The Papaspyrou/Feinendegen article describes the basic principles of BNCT, and the possible use of cold neutrons. While the Harling et al. article indicates that the reactor shown in the article is an upgraded model, I believe it is possible to provide apparatus which will make such therapy accessible to more people at less cost and with consider:ably lower side effects than appears possible with the MITR-II equipment, for example.
The current BNCT experimental applications by others of which I am aware do beam optimization outside of the reactor, starting with a neutron leakage spectrum, which by itself is inadequate for BNCT. A beam modifying "filter" is then applied to prepare the beam for BNCT. According to my concept, neutronics optimization is to be accomplished within the reactor vessel itself, resulting in a simpler and more compact design, while minimizing at the same time the side effects. An additional, more specific design criterion for minimizing side effects has been identified during the preparation of this application, which, to my knowledge, has not appeared in the literature in this form: the minimization of the overall number of neutrons in the beam, say n.sub.t. This criterion is also considered in the conceptual design of this application.
Some additional papers, Refs. 3 to 10, also describe nuclear reactor application for BNCT. These papers are as follows:
Ref. 1 "Boron Neutron Capture Therapy and Radiation Synovectomy Research at the Massachusetts Institute of Technology Research Reactor", Nuclear Science and Engineering, Otto K. Harling et al., Vol 110, pgs. 330-348, Apr. 1992.
Ref. 2 "Possible Use of Cold Neutrons for Boron Neutron Capture Therapy", Nuclear Science and Engineering, M. Papaspyrou and L. E. Feinendegen, Vol 110, pgs. 349-354, Apr. 1992.
Ref. 3. "Performance of the Currently Available Epithermal Neutron Beam at the Massachusetts Institute of Technology Research Reactor (MITR-II)", Progress In Neutron Capture Therapy for Cancer, Edited by B. J. Allen et al., Plenum Press, New York, 1992, pgs. 53-56.
Ref. 4. "Installation and Testing of an Optimized Epithermal Neutron Beam at the Brookhaven Medical Research Reactor (BMRR)", R. G. Fairchild et al., Neutron Beam, Development, and Performance for Neutron Capture Therapy, Edited by O. K. Harling et al., Plenum Press, New York, 1990, pgs. 185-199.
Ref. 5. "Epithermal Neutron Beam Design for Neutron Capture Therapy at the Power Burst Facility and the Brookhaven Medical Research Reactor", Floyd J. Wheeler et al., Nuclear Technology, Vol. 92, October, 1990, pgs. 106-117.
Ref. 6. "Demonstration of three-dimensional deterministic radiation transport theory dose distribution analysis for boron neutron capture therapy", by David W. Nigget al., Medical Physics, Vol. 18(1), Jan/Feb 1991, pgs. 43-53.
Ref. 7. "Reactor physics design for an epithermal neutron beam at the Power Burst reactor Facility", F. J. Wheeler et al., Strohlenther. Onkol., Vol. 165, 1989, pgs. 69-71.
Ref. 8. "Conceptual Physics Design of an Epithermal-Neutron Facility for Neutron Capture Therapy at the Georgia Tech Research Reactor", David W. Nigg and Floyd J. Wheeler, published by Idaho National Engineering Laboratory according to its INEL BNCT Program, under U.S. Government DOE Contract No. DE-AC07-761DO1570.
Ref. 9. "Conceptual Design of a Medical Reactor for Neutron Capture Therapy", William A. Neuman and James L. Jones, Nuclear Technology, Vol. 92, Oct. 1990, pgs. 77-92.
Ref. 10. "Investigation of a Nuclear Reactor for Cancer Therapy", Yutaka Mishima, Report by the Special Institute for Cancer Neutron Capture Therapy, Kobe University, Japan, March 1990.
Most of these papers describe beam preparation activities at four reactors:
MITR-II (Ref. 3; this is a different version of Ref. 1) PA1 BMRR (Brookhaven Medical Research Reactor, Refs. 4 to 6) PA1 PBF (Power Burst Facility, Refs. 5 and 7) PA1 GTRR (Georgia Tech Research Reactor, Ref. 8)
Beam Optimisation at a fifth reactor (the European High Flux Reactor in Petten, Netherlands) follows the same principles; see Ref. 9, p. 78. The Ref. 9 paper describes a concept for a multiple treatment room facility associated with a reactor using a low-enriched uranium-zirconium hydrite fuel and associated filters using solid plates, non-circulating D.sub.2 O, and water for coolant. The concept is to provide a low power reactor and use "power cycling" such as 10 minutes at full power and 50 minutes standby at 1% power, for example. Simultaneous treatment of patients in several treatment rooms would be accomplished during all or part of the full power mode, the duration being selectable to tailor treatment to each patient's need, and controlled by beam shutters.
What all these efforts have in common is that they start with an unsuitable neutron spectrum, consisting primarily of thermal neutrons, and then employ bulky external "filters" to shape the neutron spectrum for BNCT application. The primary task of these arrangements is to "filter" out the undesirable thermal neutron and to reduce the fast neutron and .gamma.-ray components of the leakage spectra.